Hybrid Planar–Twisted Chair‐Shaped Indoline Donor Enabling Bright Molecular and Aggregated State Near‐Infrared Emission

Abstract Organic near‐infrared (NIR) fluorophores with donor–acceptor (D–A) architectures have emerged as a preeminent paradigm in optoelectronic engineering and biomedical applications. However, conventional D–A NIR emitters often suffer from aggregation‐induced quenching or weak absorption owing to the use of planar (e.g., carbazole) or highly twisted (e.g., triphenylamine) donor units, which impairs their versatile utility in molecular and aggregated states. Herein, we proposed a unique chair‐shaped indoline donor ( c ID) with a hybrid planar–twisted conformation, which affords bright various states (solution, solid, microspheres, nanoparticles, and films) NIR emission spanning 650–1200 nm, with tails extending to 1600 nm. The c ID donor promotes electron localization, imparting higher oscillator strength and a smaller HOMO–LUMO energy gap to the designed NIR fluorophores, which together enhance light‐harvesting capacity and induce red‐shifted emission. Meanwhile, the sterically hindered nonconjugated group in c ID effectively restricts low frequency vibration‐induced non‐radiative decay, as evidenced by the reduced reorganization energy and Huang–Rhys factor in both isolated and crystalline phase. Through structurally π‐conjugation extension, these NIR fluorophores exhibit robust various‐state NIR‐I (photoluminescence quantum yields up to 67.8% and brightness up to 15668 M −1 cm −1 ) and NIR‐II emission, which allows diverse advanced applications in porous ceramic damage detection, stimulated emission depletion (STED) microscopy, and NIR‐II vascular imaging, thereby positioning c ID as a versatile toolkit to create a novel NIR dye library for biomedical and optoelectronic field.